<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<meta name="viewport"
	      content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title>Document</title>
</head>
<body>
<script>
function * show() {
    alert("a");

    let a = yield ;

	alert("b");

	alert(a);//5
}
let gen = show();
gen.next(12);   //第一个next没办法传参
gen.next(5)
</script>
</body>
</html>